Method for attaching pulse encoder to motor and motor attached with same

ABSTRACT

When a pulse encoder is attached to a motor, first a stationary coded plate (20) is temporarily held on one end (18) of a motor housing (12) to modify a deviation thereof during a rotation of the motor housing (12) around an output shaft (14) of the motor, then a gauge (50) is interposed between said stationary coded plate (20) and a rotary coded plate (48) to separate them from the other by a prescribed distance, and next the output shaft (14) is rotated relative to the motor housing (12) to modify a deviation of the rotary coded plate (48) temporarily fixed to the sleeve member (42). According to the above method, the pulse encoder is accurately and efficiently attached to the motor.

TECHNICAL FIELD

The present invention relates to a method for attaching a pulse encoderto be built in a motor to the motor, and relates to the motor having thepulse encoder attached thereto by that method.

BACKGROUND ART

A method whereby a rotary coded plate is first attached and then astationary coded plate is attached on the basis of the rotary codedplate, is adopted in the prior art as a method for attaching the pulseencoder to the motor. Namely, the rotary coded plate is attached to oneend of an output shaft of the motor so as to be at a right angle to acentral axis of the shaft and centrally aligned. On the other hand, thestationary coded plate is fixed upon a plate member having a recess formounting a light sensor, by an adhesive agent, and the position of thelight sensor is adjusted in two dimensions (in a plane) with regard tothe positions of slits of the stationary coded plate, and the lightsensor is fixed by screws. A spacer is interposed between the plateelement and one end of the motor so that the plate element having thelight sensor and the stationary coded plate are separated from saidrotary coded plate by a predetermined clearance distance, and theposition of the plate element is adjusted in two-dimensional directionsso that slits of the rotary coded plate are coaxial with slits of thestationary coded plate, and the plate element is fixed to one end of themotor by screws.

Conventionally, a pulse encoder is built in a motor in the mannermentioned above, but it is time-consuming to attach the pulse encoder tothe motor in such a manner, and an accurate attachment thereof cannot beefficiently achieved. Namely, a working step is necessary whereby thestationary coded plate is mounted separately from one end of the motorand spaced from the first mounted rotary coded plate by a predeterminedclearance distance. This clearance distance must be made shorter as aresolution power of the pulse encoder increases, and thus the adjustmentwork becomes more difficult. Furthermore, the position of the plateelement having the stationary coded plate must be adjusted in twodimensional directions so that the positions of slits of the stationarycoded plate are set coaxially with the positions of slits of the rotarycoded plate.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to solve the aboveproblems by providing a method for building each element of a pulseencoder in a motor accurately and efficiently, and thus provide a motorwith the pulse encoder built therein by the above method.

In view of the above-mentioned object, the present invention provides amethod for attaching a pulse encoder to a motor, characterized bytemporarily attaching a stationary coded plate having a circular trackpattern coaxial with slits thereof and provided with a light sensor,onto one end of a motor housing formed at a right angle to a centralaxis of an output shaft of the motor; rotating the motor housing aroundthe output shaft to centrally align the stationary coded plate accordingto a deformation of the circular track pattern caused by a centraldeviation during rotation of the stationary coded plate; preciselyfixing the stationary coded plate onto the one end of the motor housing;and inserting a sleeve attached the rotary coded plate thereon upon theoutput shaft from the one end, while interposing a clearance gaugebetween the stationary coded plate and the rotary coded plate and fixingsame, to thereby set a clearance between the stationary coded plate andthe rotary coded plate.

Furthermore, the present invention provides a motor having a pulseencoder attached thereto by the above method.

According to the above-mentioned method, the stationary coded plate canbe centrally aligned by pushing same in one radial direction of thecircular track pattern, and then the relative positioning of the rotarycoded plate and the stationary coded plate can be accurately achieved byonly the steps of, putting the clearance gauge on the stationary codedplate positioned by the central aligning; inserting the sleeve havingthe rotary coded plate attached thereon onto the output shaft; andfixing the sleeve to the shaft to cause the rotary coded plate to abutagainst the clearance gauge. Thus a motor having a highly accurate pulseencoder can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing the attachment of a stationary coded plateof the pulse encoder according to the method of the present invention;

FIG. 2 is a longitudinal local sectional view of FIG. 1 taken along theline II--II;

FIG. 3 is a longitudinal local sectional view showing one state of theworking process whereby a rotary coded plate is attached on the basis ofthe stationary coded plate; and,

FIG. 4 is a plan view of a spring plate ring.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIGS. 1 and 2, a C shaped annular portion 16 is integratedwith a rear end 12 of a motor housing. An end surface 18 of the annularportion 16 has been ground at a right angle to a central axis 10 of anoutput shaft 14 of the motor holding the shaft 14. On the other hand, aplate 22 having light sensors is adhered on an annular coded plate 20 tobe fixed so that the light sensors correspond to slits 36 of the fixedstationary coded plate 20.

The stationary coded plate 20 having the light sensor plate 22 adheredthereon is placed on the end surface 18 of the C shaped annular portion16 of the motor housing which is fixed to a work table (not shown) in astate such that a front end of the shaft 14 of the motor is directeddownward. A triangular support plate 24 holding the other end of a halfcylindrical member 26 provided with a threaded portion on the outersurface at least near one end of the member at one vertex portionthereof, is inserted through an open side of the C shaped annularportion 16 so that the half cylindrical threaded member 26 surrounds theshaft 14. Then, the remaining two vertex portions are fixed to the rearend portion 12 of the motor housing by screw members 32. After themember 26 is thus immovably fixed, the stationary coded plate 20 istemporarily pushed onto the end surface 18 of the annular portion 16 andheld by a nut 30 extending through central hole 38.

The motor housing is rotated around the fixed shaft 14 in a state suchthat the stationary coded plate 20 is temporarily fixed asabove-mentioned, and a circular track 34 for a central alignment isdrawn on the stationary coded plate 20 coaxially with the slits 36. Itcan be accurately seen from the above, by a microscope, that thecircular track 34 during rotation projects most at a position crossingan imaginary radius line extending through a center of the circulartrack 34 from a point of the central axis 10, and retracts most at theopposite position when the stationary coded plate 20 temporarily fixedto the motor housing is rotated with the motor housing, if the center ofthe circular track 34 is not positioned on the central axis 10 of theshaft 14. Therefore, a central alignment is achieved only by pushing thestationary coded plate 20 having a circular outer periphery in thedirection of the center deviation by the amount of deviation, calculatedon the basis of the amounts of the projection and the retraction, by ajig tool (not shown). Then, the stationary coded plate 20 is preciselyfixed on the end surface 18 of the annular portion 16 by coating anadhesive including an epoxy resin, etc., around the stationary codedplate 20.

Then, the triangular support plate 24 having the half cylindrical member26 is removed by removing the nut 30 and the screws 32. Next, referringto FIG. 3, the method for attaching a rotary coded plate on the basis ofthe stationary plate 20 will be explained hereinafter.

A clearance gauge 50 having a prescribed thickness is placed upon thestationary plate 20. On the other hand, the rotary coded plate 48 istemporarily held by pressure from a spring plate ring 56 (refer to FIG.4) operating to apply the spring force thereof onto a shoulder 46 of asleeve 42, which shoulder has a high flatness. The sleeve 42 is providedwith a hole 44 having a prescribed depth, to enable a press-fitinsertion onto a smaller portion 40 of the rear end of the shaft 14 atone end thereof, and with a smaller portion 52 on the other end thereofto form the shoulder 46. The sleeve 42 temporarily holding the rotarycoded plate 48 is inserted onto the smaller portion 40 of the shaft 14,the portion 40 being coated with an adhesive, until the rotary codedplate 48 abuts against the gauge 50, and left in this state until theadhesive is hardened. Then, the gauge 50 is removed, and the rotarycoded plate 48 is centrally aligned in the same manner as the stationarycoded plate 20. Namely, a circular track for a coaxial centering witheach slit is also drawn on the rotary coded plate 48. This centering isachieved by fixing the motor housing and by observing through amicroscope the trace of a circular track when the output shaft isrotated. The size of a central hole 54 of the rotary coded plate 48 is alittle larger than the size of the smaller portion 52 of the sleeve 42,and is smaller than the size of the shoulder, so that the rotary codedplate 48 is placed on the shoulder 46 such that it can be moved in aradial direction by a jig tool when it is to be centrally aligned. Afterthis centering is completed, an adhesive is filled therein from abovethe spring plate ring 56 to fix the rotary coded plate 48 to the sleeve42. A hole 58 having a small diameter formed along an axis of the sleeve42 allows air to be exhausted when the sleeve 42 is inserted onto thesmaller portion 40 of the shaft 14.

In this embodiment, the positioning of the light sensor plate 22 inalignment with the stationary coded plate 20 is easily effected becausethe former is directly fixed to the latter by an adhesive. Further, thepositioning (centering) of the sleeve 42 in alignment with the rotarycoded plate 48 can be achieved by a separate process because the fittingof the sleeve 42 and the smaller portion 40 of the shaft 14 can beaccurately carried out. In such a case, the work efficiency forattaching the pulse encoder to the motor is further increased.

The following is apparent from the foregoing description. The stationarycoded plate is mounted accurately at a right angle to the central axisfor rotation because the stationary coded plate is placed on the largeend surface of the motor housing, which surface is machined at a rightangle to the central axis of the shaft of the motor, and the centeringcan be achieved only by pushing the stationary coded plate in thespecific radial direction of the circular track, because the circulartrack for centering is drawn on the stationary coded plate so that anycentral deviation of the circular track is observed during rotation ofthe motor housing. Namely, the centering can be achieved only by anadjustment thereof in a one-dimensional direction of the radius thereof.On the other hand, the clearance between the rotary coded plate and thestationary coded plate can be set only by abutting the rotary codedplate temporarily held on a sleeve against a prescribed gauge placed onthe stationary coded plate mounted in the above-mentioned manner. Thecentering of the rotary coded plate also can be achieved only by anadjustment thereof in a one-dimensional direction of the radius using acircular track for centering. Accordingly, the pulse encoder can bebuilt into the motor accurately and efficiently, and thus a motor havingthe pulse encoder with a high detection performance can be provided.

We claim:
 1. A method for attaching a pulse encoder to a motorcomprising the steps of:(a) fixing a front end of a shaft of said motorto a work table directed downwardly such that an output shaft of saidmotor projects upwardly at a rear end within a portion of a housing ofsaid motor having a plane end surface formed at a right angle to an axisof said output shaft; (b) fixing a stationary coded plate of said pulseencoder to said motor housing plane end surface by a process whichincludes:temporarily attaching said stationary coded plate to saidhousing surface such that a circular track pattern on said stationarycoded plate surrounds said output shaft axis, rotating said motorhousing around said output shaft to determine a deviation of a center ofsaid circular track pattern from said axis, moving said stationary codedplate to make said circular track precisely centrally align with saidaxis, and then adhesively fixing said stationary coded plate to saidhousing plane end surface; and (c) attaching a rotary coded plate ofsaid pulse encoder to said output shaft by a process whichincludes:inserting a sleeve, having said rotary coded plate attachedthereon, upon said output shaft from said rear end with a clearancegauge interposed between said stationary coded plate and said rotarycoded plate, moving said sleeve onto said output shaft until said rotarycoded plate abuts said clearance gauge in contact with said stationarycoded plate, and adhesively fixing said sleeve to said output shaft. 2.A method as recited in claim 1 which includes the further step:(d)attaching a light sensor of said pulse encoder to said stationary codedplate by an adhesive.
 3. A method as recited in claim 1 wherein saidprocess for attaching said rotary coded plate further includes rotatingsaid shaft to determine a deviation of a center of a circular trackpattern on said rotary coded plate from said output shaft axis, movingsaid rotary coded plate on said sleeve to precisely centrally align saidcenter with said axis, and adhesively fixing said rotary coded plate tosaid sleeve.
 4. A method as recited in claim 3 which includes thefurther step:(d) attaching a light sensor of said pulse encoder to saidstationary coded plate by an adhesive.
 5. A motor having a pulse encoderattached thereto, comprising:a motor having a housing and an outputshaft, one end surface of the motor housing being formed as a plane at aright angle to a central axis of the output shaft of the motor, anannular stationary coded plate having a circular track pattern formedthereon coaxial with slits thereof, said stationary coded plate beingfixed onto said plane end surface by an adhesive, coaxially with saidcentral axis, a sleeve member fixed onto said output shaft by anadhesive through a central hole of said annular stationary coded plate,and a rotary coded plate with a circular track pattern fixed onto ashoulder of said sleeve member forming a step, coaxially with saidcentral axis.
 6. A motor having a pulse encoder according to claim 5,wherein said sleeve member has a small hole communicated with a holeaccepting said output shaft.
 7. A motor having a pulse encoder accordingto claim 5, wherein a spring plate ring is engaged with an end portionof said sleeve member to press said rotary coded plate onto saidshoulder of said sleeve member.
 8. A motor having a pulse encoderaccording to claim 7, wherein said sleeve member has a small holecommunicated with a hole accepting said output shaft.